Thermoelectrically refrigerated apparatus



T. M. ELFVlNG 3,100,970 THERMOELECTRICALLY REFRIGERATED APPARATUS FiledMarch 14, 1961 4 Sheets-Sheet 1 INVENTOR. More M [/fV/ng.

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Aug. 20, 1963 r T. M. ELFVING 3,100,970

THERMOELECTRICALLY REFRIGERATED APPARATUS Filed March 14. 1961 4Sheets-Sheet 2 V INVENTOR. 7/20/"9 M [A r/ny- 4 Sheets-Sheet 3 FiledMarch 14, 1961 INVENTOR. Mare M f/f m FIE 7 Aug. 20, 1963 T. M. ELFVING3,100,970

THERMOELECTRICALLY REFRIGERATED APPARATUS Filed March 14, 1961 9 4Sheets-Sheet 4 IIE 4 IN VEN TOR. More M [A /m5! United States Patent3,100,970 TI IERMQELECTRICALLY REFRIGERATED APPARATUS Thore M. Elfving,433 Fairfax Ave, San Mateo, Calif. Filed Mar. 14, 1961, Ser. No. 95,59924 Claims. (Cl. 623) The present invention relates to thermoelectricallyrefrigerated apparatus such as refrigerators or other cooled orrefrigerated spaces, compartments and the like, and particularly inwhich thermoelectric heat pump equipment is used for absorbing heat andlowering the temperature of the refrigerated space.

it is a general object of the present invention to provide improvedthermoelectrically refrigerated apparatus, simple in construction andefficient in operation.

Another object of the invention is to provide improvedthermoelectrically refrigerated apparatus including a compartment oflower temperature for ice freezing or storage of frozen food or otherpurposes in connection with such a refrigerated space.

It is still another object of the present invention to provide animproved thermoelectric household refrigerator.

It is a further object of the present invention to provide athermoelectrically refrigerated apparatus having compartments maintainedat different temperatures.

These and other objects of the invention will be understood from thefollowing description when read in connection with the accompanyingdrawings in which FiGURE 1 is a perspective view partly in section of athermoelectrically refrigerated apparatus according to the invention;

FIGURE 2 is an enlarged view of the low temperature compartment ofFIGURE 1;

FIGURE 3 shows a thermoelectric refrigerator with a freezer compartmentbelow the main refrigerated space with separate thermoelectric heatpumping equipment; and

FIGURE 4 shows another embodiment of a refrigerator with separatefreezer compartment and with an improved heat dissipating warmingcompartment on top of the cabinet.

Referring to FIGURE 1, there is shown a perspective view, partly brokenaway, of a combined thermoelectric refrigerator and warmer. Therefrigerator and warmer include a horizontal assembly of thermoelectricmodules 8 with the cold junction side facing downwards and the hotjunction side facing upwards. The modules 8 preferably have both sidesin thermal contact with anodized and grooved aluminum protective andheat equalizing plates. The plates may be formed and placed in thermalcontact in accordance with the teaching in copending applicationentitled Thermoelectric Heat Pump Assembly, filed February 6, 1%1,Serial No. 87,360, now Patent No. 3,075,360.

The protective and heat equilizing aluminum plates 9 on the cold sideare in direct thermal contact with the upper horizontal portion 19 of adouble-walled aluminum lining 11. The lining 11 includes spaced aluminumplates or sheets which are bonded or sealed at the edges and includeinterior bonded areas 13 to form a multitude of gas or liquid passagesor channels 12 over the entire lining. The use of such double-walledusually roll bonded, plates or linings in connection with thermoelectricrefrigeration is shown in my copending application Serial No. 47,161,filed on August 3, 1960. The inside space of the lining 11 is partlyfilled with a volatile liquid which serves as a heat transfer medium asdescribed in copending application Serial No. 47,161 above.

The lining 11 can be made by bending a long doublewalled bonded plate infour places as illustrated. The

3,100,970 Patented Aug. 20, 1963 "Ice is directly in contact withanother double-walled hermetic system 17 similarly bent to form anenclosed space and provided with gas or liquid passages as illustrated.The double-Walled system 17 is partly filled with a volatile liquid. Thedouble-walled system 17 serves as the heat dissipating surface for theair cooling of the hot junctions of the modules 8. The space enclosed bythe plate 17 can be closed off at the rear and provided with a lid ordoor at the front to form a warmer for various purposes. Preferably, theplate 17 is not insulated on the outside.

It can also be left open, as illustrated in the figure, to form a partof a duct for cold air. For example, it may fonma portion of the airconditioning duct in an automobile. Cold air will then pass over theinside wall surfaces of the double-walled plate 17 whereby the hotjunctions of the modules are effectively cooled and the air warmed. Theduct is preferably insulated on the outside.

Because of the nature of the heat transfer systems represented by thedouble-walled plates 11 and 17, both will assume a substantially eventemperature over the whole of their surfaces. The temperature of plate11 will be close to the cold junction temperature, whereas thetemperature of the plate 17 will be close to the hot junctiontemperature of the modules 8. The doublewalled plates 11 and 17 can beexpanded on both sides or on one side only, preferably being smooth onthe side in thermal contact with the protective aluminum plates 9 and16.

The modules ll are provided with direct current by the lead 1 8. Thepower may be obtained from a direct current power supply connected to asource of A.-C. power; The current is regulated by the variable resistor19.

Referring to FIGURE 1, there is provided a low tempeuature compartment20 with an ice tray 21. The lining 2,2 of the low temperaturecompartment is cooled by thermoelectric modules 23 having their coldjunctions in direct thermal but not electrical contact with the lining22. The hot junctions are in thermal contact with the upper portion ofthe double-walled lining 11 through the heat equalizing and protectivealuminum plate 24.

The modules 23 form a first stage heat pumping system indirectly cooledby the modules 8 which in relation to the modules 23 constitute a secondstage heat pumping system. Thus, according to the invention, thethermoelectric modules 8 are used both as a single stage heat pump forabsorbing heat from the compartment 14 and as second stage heat pumpingmeans in combination with a first stage heat pump for creatingtemperatures below freezing in the low temperature compartment 20. Thefirst stage modules 23 can be supplied with direct current parallel withthe modules 8 over a separate variable resistor 25.

FIGURE 2 shows in sectional view the low temperature compartment 20. Theice tray 21 is placed on the metal lining 22 which in the ceiling is indirect thermal contact with the cold junctions of the modules 23. Themetal lining 22 of this compartment can be of plain sheet metal,preferably of copper or aluminum. It can also be of the double-walledtype and filled with a heat transfer medium for equalizing thetemperature all over the lining. The

modules 23 are on their hot junction side provided with a heatequalizing, preferably anodized and grooved, plate 24 which is gluedto'the uneven underside of the horizontal portion ll) of the lining 11,where the channels 12 are at least partly'filled with volatile liquidcondensate. The heat from the hot junctions of the modules 23 willevaporate the volatile liquid and the heat from V the first stagemodules will be delivered over the whole area of the plate 9 and thecold junction side of the modules 8. The ice freezing or low temperaturecompartment 20 can, according to the invention, be provided with asuitable insulation 26 as shown in the drawing. In FIGURE 2 is alsoshown a filling valve 27 which serves to aid in filling thedouble-walled'lining 11 with a volatile liquid.

The firststage modules 23 are in the figure placed in thermal contactwith the upper portion of the lining 11, in other words in contact withthe heat dissipating portion of the hermetic heat transfer systemattached to the cold junctions of the modules 8. The first stage modules23 can, according to the invention, also be placed at the lower portionof said heat transfer system, for instance, on the floor portion of thelining '11. In both cases the heat from the hot junctions of'the firststage thermoelectric heat pump is carried to the cold side of themodules 8 as in an ordinary cascade coupling with the dilference,however, that the second stage modules 8, ac-

, cording to the invention, have a much larger pumping capacity thanneeded for the first stage heat pump only and therefore can serve alsoas directcooling means for the refrigerator itself.

The energy supplied to the second stage modules 8 is, according to theinvention, several times greater than the energy supplied to the firststage heat pump =23. A ratio of between '10 and 12 to l or more isrepresentative of normal conditions in a household refrigerator whereonly ordinary ice freezing is wanted. In a refrigerator where also a lowtemperature compartment for the keeping of frozen food is provided, anenergy ratio of between 4 and 8 to 1 is suitable, depending upontherelative size of the compartments for medium and low temperatures. Thetotal energy necessary is naturally dependent upon the size of thecabinet, its insulation and the prevalent ambient temperature as wellasupon the factor of merit (Z-factor) of the thermoelectric materialused, and the number and size of the thermocouples. The second walledpanel with a great multitude of interconnected cavities or hollow spacesevenly dispersed over the whole lining which forms the side walls andceiling and door in the refrigerator commodity compartment. The edges 35of the lining 33 are firmly bonded together without any outlet exceptfor a filling valve 36 for filling the cavities in the double-walledlining 33 partly with a heat transfer medium like Freon.

The upper horizontal portion or ceiling of the lining 33 is on itsoverside in thermal contact with the cold junction side of thethermoelectric couple assemblies 38 supplied with 11-0 current from apower supply 39 through the leads all over the thermostat 41, which canbe of the intermittent operating type, with a sensitive bulb 42 placedin the commodity space 31. The thermostat acts upon the A.-C. inputleads to the rectifier 39 as de-,

scribed in .my previously mentioned copending application Serial No.47,161. The hot junction sides of the thermoelectric assemblies 3?, arein contact with a heat dissipating fin radiator 43 with forced aircirculation by the fan 44. The fan and the radiator are provided with aprotective cover 45. The heat dissipating means in contact with the hotjunctions 38 can be of any type, for

- figure is shown metal tray shelves 48, preferably of anodized groovedaluminum, in thermal contact with the cold junctions and serving asradiators for ice freezing trays 49. The space 5% under the ice freezersserves as storage 2 room for frozen food or similar purposes.

stage? thermocouples with the double function of providing mediumtemperature cooling means for the direct cooling of the mainrefrigerator space and of second stage heat pump in an indirect cascadesystem has to operate with a relatively high temperature differencebetween the cold and the. hot junctions, say a At of 35-45 C.

The thermoelectric couple assemblies 47 may be supplied with D.-C.current separately from a smal rectifier '51 through the leads 52 overthe smal variable resistor 53.

As'previously mentioned, an automatic temperature control of thedescribed system is carried out by means of a thermostat forintermittent energization of the main heat pump, represented by themodules 38, with the sensitive bulb 42 of the thermostat placed in thecompartment 31. Because of the small ratio of energy supplied to thefirst stage heat pump, it can, according to the invention, stay on allthe time in order to keep a constant temperature in the freezercompartment. The firststage thermocouples will operate normally alsowhen the energy supply to the second stage heat pump is tempoin an aircooled application. The corresponding coeiilcapacity is adequate for icefreezing and a low temperature storage place in a medium sizerefrigerator. The arrangement of a thermoelectric first stage heat pumpindirectly connected to the main heat pump equipment, according to theinvention, has proven very efficient and economical with a minimum oflosses.

' FIGURE 3 shows another embodiment of a refrigerator according to theinvention with separate thermoelectric heat pumps for a commodity spaceabove freezing and for a freezer compartment. The commodity space 31with shelves 32 has a double-Walled metal lining 33 with a multitude ofbonds 34 between the two Walls in the form of small round patches, spotsor joined surfaces of any configuration forming a pressure resistantdoublerarily shut ofll as long as the temperature of the heat transfersystem represented by the lining 33 is not raised more than a fewdegrees. The temperature of the lining 33 will be kept fairly constantby the accumulative efiect of the content in the refrigerated space andshorter cutoff intervals of the main heat pump will, therefore, not.

afiect the refrigeration of the freezer compartment which is animportant feature of the present invention. In combination with theautomatic temperature control of the food compartment 3 1, the lowtemperature compartment temperature is preferably provided with a handregulated temperature control comprising the small variable resistor 53in series with the first stage thermocouples which, thus, arepermanently but variably energized. When the invention is applied to arefrigerator for an automobile or boat, also the main heat pump can beprovided with a variable resistor in series with the thermocouples toadjust the heat pumping capacity according to the ambient requirements,as illustrated in FIGURE 1. I

The thermoelectric assembly 47 dissipating the heat from its hotjunctions to the bottom portion of the doublewalled-lining 33 operateswith a small temperature difference between the hot and the coldjunctions. Under junctions.

normal operating conditions, the hot junctions can be kept at atemperature of '|-10 C. or lower and can produce freezing temperaturesof C. or lower with a At of only C., which for a Z-factor of 3 means acorresponding COP close to 2 and a refrigerating efiect twice as largeas the energy input. The coupling of the low temperature first stagethermocouple assemblies indirectly to the main heat pump assembly overthe lining 33 creates very favorable conditions with a minimum of lossesto the first stage low temperature junctions. The indirect coupling ofthe two stages, according to the invention, thus offers maximumefliciency, simplicity and flexibility.

The thermoelectric freezer compartment design illustrated by FIGURE 3can, according to the invention, also be used in combination with otherrefrigeration processes, such as compressor refrigeration or absorptionrefrigeration. Bothcompressor refrigeration and absorption refrigerationrapidly lose in efliciency at lower evaporator temperatures. The loss isdue mainly to the expansion of the refrigerant gases at lowertemperatures. Thermoelectric refrigeration is independent of thisphysical law but is instead sensitive for large temperature differencesbetween the cold and the hot junctions. It is, therefore, technicallyand economically advantageous to combine, for instance, compressorrefrigeration at medium temperature operation with a thermoelectric heatpump for refrigeration effects at lower temperatures.

A refrigerator with two compartments of difierent temperatures, asdescribed in FIGURE 3, offers an example of such a combination of twodifferent refrigeration processes. The double-walled lining 33 in FIGURE3 can, according to the present invention, be connected at each of theedges 35 with the low pressure side of a compressor so that the lining33 forms an evaporator with an expansion valve at one end and a suctionline at the other. The compressor can be operated at a back pressurecorresponding to the desired temperature of the main commodity space,say at an evaporator temperature of +1 to 2 C. The double-walled lining33 is as before partly filled with refrigerant. The thermoelectric heatpump equipment for the freezer compartment 46 can be arranged in exactlythe same way as previously described. In this way, the compressor canoperate at a high back pressure with maximum efficiency while thethermoelectric heat pump takes the temperature down to say 20 C. Theheat exchange between the thermoelectric heat pump 47 and thedouble-walled lining 33 will take place in the same way regardless ifthe lining 33 is cooled thermoelectrically or by a compressor. Thetemperature of the compartment 31 can in both cases be regulated by athermostat connected to the A.-C. lead to intermittently energize theassociated D.-C current supply or motor as the case may be. The freezercompartment heat pump stays on all the time except for defrosting andother similar interruptions. The freezer compartment can be defrosted byswitching the D.-C. current to the thermoelectric heat pump 47 so thatthe cold junctions become hot This defrosting operation can be handregulated or automatic in any known way.

The combination of a medium temperature Freon system in the form of adouble-walled lining or plate evaporator with a thermoelectric heat pumpin thermal con tact with said lining and plate on its hot junction side,according to the invention, can be given a multitude of forms. Thedouble function of the volatile liquid system to provide direct mediumtemperature cooling of a refrigerated space and to serve as a heat sinkfor a low temperature thermoelectric heat pump system is characteristicof the present invention. The invention can be applied to all types ofrefrigerators or similar devices where more than one working temperatureis desired.

In FIGURE 4 is shown a household refrigerator with a freezer compartmentas in FIGURE 3 but with another type of final heat dissipating surfacein the form of a semi-closed warming compartment. The main thermocoupleassembly 61 is as before placed with its cold side against the upperhorizontal portion of the double-walled lining 62 which encircles themedium temperature refrigerator compartment 63 as previously described.A preferably anodized and grooved aluminum plate 64 placed between thelining 62 and the thermocouple assembly 61 serves to establish thethermal contact between the cold junctions and the lining. Under thefloor of the compartment 63 is arranged a freezer compartment 65 cooledby the first stage thermoelectric modules 66 dissipating their heat onthe hot junction side to the lining 62 as described in connection withFIGURE 3.

The main thermoelectric assembly 6; is on its hot junction side inthermal contact, over another equalizing plate 67, with the heatabsorbing portion 68 a double-walled heat transfer lining 69, partlyfilled with volatile liquid forming a semi-closed heat dissipatingwarming chamber 70 as illustrated by the figure. The lower heatabsorbing part 68 is placed in a hole or cut out in the ceilinginsulation 71 and has approximately the same area as the thermocoupleassembly 61. "In this way, full insulation thickness can be providedbetween the cold lining 62 and the warm heat dissipating lining 69except for the contact area of the thermocouple assembly. The coldlining 62 can preferably be insulated from the compartment 63 in theceiling portion thereof by means of an insulation layer 72 which servesto prevent drippage of condensate from the ceiling and also reduceslosses when the thermoelectric assembly 61 is deenergized and thetemperature between the cold and hot junctions is equalized. The

' void formed in the floor of the chamber 76! by the protruding portion68 of the lining 69 is covered by a screen 73. The floor and the screen73 can preferably be covered by a suitable floor rack, not shown in thefigure, to prevent direct contact between warm objects and the lining69.

Instead of the heat dissipating linings shown above for air cooling ofthe refrigerator, one can provide simple double-walled plates in contactwith the hot junctions of the main thermocouple assembly for watercooling of the heat pump. Such an arrangement would be especiallysuitable for shipboard refrigeration.

I claim:

1. A refrigerator comprising a first refrigerating chamber, a secondrefrigerating chamber of a higher temperature than said firstrefrigerating chamber, at least a first and at least a secondthermocouple assembly, each having hot and cold junctions, a one-wayheat transfer system comprising, a double-Walled member partly filledwith a refrigerant, said double walled member having a heat absorbingevaporator portion and a heat dissipating condenser portion at a higherlevel than the evaporator portion, said condenser portion being indirect thermal contact with the cold junctions of said secondthermocouple assembly, said evaporator being in heat exchange rela .tionto said second refrigerating chamber, the hot junctions of said firstthermocouple assembly being in direct thermal contact with said doublewalled member, the cold junction side of said first thermocoupleassembly being in heat exchange relation with said first refrigeratingchamber for cooling the same, means for dissipating heat from the hotjunction side of said second thermocouple assembly, and means forsupplying said first and second 3. A refrigerator as in claim 1 whereinthe first refrigerating chamber is located directly under the secondrefrigerating chamber with the double-walled member forming the floor ofthe second refrigerating chamber and the ceiling of the firstrefrigerating chamber.

4. A refrigerator as in claim 1 wherein said first refrigeration chamberis within the second refrigeration chamber.

5. A refrigerator as in claim 2 additionally including separate secondpower supply means for supplying direct current energy to said firstthermocouple assembly.

6. A refrigerator as in claim 1 wherein said means for dissipating heatfrom the hot junction side of said second thermocouple assemblycomprises a double-walled lining, partly filled witha refrigerant.

7. A refrigerator comprising a first refrigerating chamber, a secondrefrigerating chamber of a higher temperature than-said firstrefrigerating chamber, a double-walled member forming ceiling, floor andat least one wall of said second refrigerating chamber, a refrigerantheat transfer medium inside said double-walled member, the

'floor and wall portions of said double walled member comprising theheat absorbing portion of a one-way heat transfer system, the ceilingcomprising the heat dissipating portion of said one-way heat transfersystem, first and second thermocouple assemblies each having hot andcold junctions, the hot junctions of said first thermocouple assembly indirect thermal contact with the heat absorbing portion of saiddouble-walled member, the cold junction side of said first thermocoupleassembly in heat exchange relation to said first refrigerating chamber,the cold junction side of said second thermocouple assembly in heatexchange relation to said heat dissipation portion of said double-walledmember, means for dissipating heat from the hot junction side of saidsecond thermocouple assembly, and means for supplying electric energy tosaid first and second thermocouple assemblies.

8. A refrigerator as in claim 7 additionally including power supplymeans for supplying electric energy in the form of direct current tosaid second thermocouple assem bly, means for supplying alternatingcurrent power to said power supply, and means for sensing thetemperature within said second refrigerating chamber comprising athermostat, said thermostat being connected to intermittently applyalternating current to said power supply to thereby maintain apredetermined temperature within said second refrigerating chamber.

9. A refrigerator as in claim 7 wherein the first refrigerating chamberis located directly under the second refrigerating chamber with thedouble-walled lining forming the floor of the second refrigeratingchamber and the ceiling of the first refrigerating chamber.

10. A refrigerator as in claim 7 wherein said first thermocoupleassembly has its hot junctions in thermal contact with saiddouble-walled ceiling of the second refriger-ating chamber and the firstrefrigeration chamber is Within the second refrigeration chamber.

11. A refrigerator as in claim 7 wherein said means for dissipating heatfrom the hot junction side of said second thermocouple assemblycomprises a double-walled lining, partly filled with a refrigerant.

12. A thermoelectric system for pumping heat from at least two differenttemperature levels comprising first and second thermocouple assemblies,a first refrigerated space in heat exchange with the cold junction sideof said first thermocouple assembly and being cooled thereby, a secondrefrigerated space of higher temperature than said first refrigeratedspace, a hermetic one-way heat transfer system comprising a heatabsorbing portion in thermal contact with the hot junction side of saidfirst thermocouple assembly and in heat exchange relationship with saidsecond refrigerated space and cooling the same, and

a heat dissipating portion at a higher level in direct thermal contactwith the cold junction side of said second thermocouple assembly, thesecond thermocouple assembly having a double function of pumping heatfrom both said second refrigerated space of higher temperature and fromthe hot junction side of said first thermocouple assembly, and means forsupplying said first and second thermocouple assemblies with electricalenergy.

13. A thermoelectric system as in claim 12 wherein the heat pumpingcapacity of the second thermocouple assembly is substantially largerthan the heat dissipation from the hot junction side of said firstthermocouple assembly.

14. A thermoelectric system as in claim 12 wherein the hot junction sideof the second thermocouple assembly is in thermal contact with anair-cooled heat dissipating fin radiator.

15. A thermoelectric system as in claim 12 wherein the hot junction sideof the second thermocouple assembly is cooled by a second hermetic heattransfer system comprising a heat absorbing portion in direct thermalcontact with said hot junction of said second thermocouple assembly anda heat dissipating portion exposed to the surrounding air. 1 V

16. A thermoelectric system as in claim 12 wherein the hermetic heattransfer comprises -a double-walled member with the walls bonded inspots to form a multitude of gas and liquid passages.

17. A thermoelectric system as in claim 16 wherein the heat dissipatingportion of said double-walled hermetic heat transfer system issubstantially horizontal.

18. A thermoelectric system as in claim 17 wherein said firstthermocouple assembly has its hot junctions in thermal contact With theunderside of said horizontal heat dissipating portion of said hermeticheat transfer system, whereby said, horizontal portion acts as both aheat absorbing and heat dissipating portion of the hermetic heattransfer system.

19. A thermoelectric system as in claim 16 wherein the heat absorbingportion of said double-walled hermetic heat transfer system is at leastin part substantially horizontal and wherein the hot junctions of saidfirst thermocouple assembly are in thermal contact with said horizontalpart of the heat absorbing portion.

20. A refrigerator comprising a low temperature refrigeration region anda refrigeration chamber of a higher temperature, refrigeration meansincluding an evaporator in heat exchange relationship with saidrefrigeration chamber for cooling the same, a thermocouple assemblyhaving hot and cold junctions with the hot junctions in direct thermalcontact with said evaporator and having its cold junction disposed toabsorb heat from the low temperature refrigeration region.

21. A refrigerator as in claim 20 wherein said low temperature.refrigenation region is within said second refrigerating chamber.

22. A refrigerator as in claim 20 wherein said low ing in thermalcontact with said member, the cold junction side of said firstthermocouple assembly being in heat exchange relation with said firstrefrigerating chamber for cooling the same, means for dissipating heatfrom the hot junction of said second thermocouple assembly having anarea in thermal contact therewith which is substantially the same as thearea of the hot junctions, and insulationmeans insulating the remainderof said heat dissipating means from the double-walled member.

24. A refrigerator comprising a first refrigerating chamber, a secondrefirigerating chamber of a higher temperature than said firstrefrigerating chamber, at least a f st and at least a secondthermocouple assembly, each having hot and cold junctions, adoublewallerl member partly filled with a liquid heat transfer medium,said member being in thermal contact with the cold junctions of saidsecond thermocouple assembly and in heat exchange relation to saidsecond refrigerating chamber, the hot junctions of said firstthermocouple assembly being in thermal contact With said member, thecold junction side of said first thermocouple assembly being in heatexchange relation with said first refrigerating chamber for cooling thesame, a double-Walled lining part-1y filled with refrigerant in thermalcontact with the hot junction side of said second thermocouple assembly,said double-Walled References (Jited in the file of this patent UNITEDSTATES PATENTS Lindcnblad June 12, 1956 Gaysowski MW 30, 1961

1. A REFRIGERATOR COMPRISING A FIRST REFRIGERATING CHAMBER, A SECONDREFRIGERATING CHAMBER OF A HIGHER TEMPERATURE THAN SAID FIRSTREFRIGERATING CHAMBER, AT LEAST A FIRST AND AT LEAST A SECONDTHERMOCOUPLE ASSEMBLY, EACH HAVING HOT AND COLD JUNCTIONS, A ONE-WAYHEAT TRANSFER SYSTEM COMPRISING, A DOUBLE-WALLED MEMBER PARTLY FILLEDWITH A REFRIGERANT, SAID DOUBLE WALLED MEMBER HAVING A HEAT ABSORBINGEVAPORATOR PORTION AND A HEAT DISSIPATING CONDENSER PORTION AT A HIGHERLEVEL THAN THE EVAPORATOR PORTION, SAID CONDENSER PORTION BEING INDIRECT THERMAL CONTACT WITH THE COLD JUNCTIONS OF SAID SECONDTHERMOCOUPLE ASSEMBLY, SAID EVAPORATOR BEING IN HEAT EXCHANGE RELATIONTO SAID SECOND REFRIGERATING CHAMBER, THE HOT JUNCTIONS OF SAID FIRSTTHERMOCOUPLE ASSEMBLY BEING IN DIRECT THERMAL CONTACT WITH SAID DOUBLEWALLED MEMBER, THE COLD JUNCTION SIDE OF SAID FIRST THERMOCOUPLEASSEMBLY BEING IN HEAT EXCHANGE RELATION WITH SAID FIRST REFRIGERATINGCHAMBER FOR COOLING THE SAME, MEANS FOR DISSIPATING HEAT FROM THE HOTJUNCTION SIDE OF SAID SECOND THERMOCOUPLE ASSEMBLY, AND MEANS FORSUPPLYING SAID FIRST AND SECOND THERMOCOUPLE ASSEMBLY WITH ELECTRICENERGY.